A unit cell as a minimum electric generation unit for a solid polymer electrolyte fuel cell (hereinafter also simply referred to as “fuel cell”) generally includes: a membrane electrode assembly including a solid electrolyte membrane and catalyst electrode layers (an anode-side catalyst electrode layer and a cathode-side catalyst electrode layer) bonded to both sides of the solid electrolyte membrane; a gas diffusion layer placed on both sides of the membrane electrode assembly; and a separator placed outside the gas diffusion layer.
Such a catalyst used in the catalyst electrode layer of a fuel cell generally includes a carbon support (having an electrically-conductive function) and a metal catalyst such as Pt supported on the surface of the carbon support. Patent Document 1 also discloses that a metal catalyst such as Pt is supported on the surface of a support mainly composed of SiO2.
In Patent Document 1, however, the SiO2 itself does not have electrical conductivity so that the electrochemical reaction may be delayed in Pt and thus the electric generation efficiency may be reduced.
When carbon or SiO2 is used for a support, there is also a problem in that the interaction between the support and the metal catalyst such as Pt performing the catalytic function is weak so that, during long term use of the fuel cell, agglomeration of the metal catalyst is occurred to reduce the surface area of the metal catalyst, and thus the electric generation efficiency may be reduced.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2002-246033
Patent Document 2: JP-A No. 2004-95263
Patent Document 3: JP-A No. 2002-246034
The present invention has been made in view of the above problems, and it is a main object of the present invention to provide a fuel cell catalyst in which a support for supporting a metal catalyst has electrical conductivity in itself and which can prevent agglomeration of the metal catalyst during long term use of the fuel cell.